Test and measurement instrument and method of switching waveform display styles

ABSTRACT

A test and measurement instrument and method of switching waveform display styles includes acquiring an electrical signal, storing peak detect data samples from the electrical signal to one or more memory devices, storing filtered data samples or unfiltered data from the electrical signal, automatically switching to a first waveform display style having the peak detect data samples configured in a first mode when a user selects the unfiltered data, and automatically switching to a second waveform display style having the peak detect data samples configured in a second mode when the user selects the filtered data samples.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No.61/105,922, filed Oct. 16, 2008, which is hereby incorporated byreference.

BACKGROUND

This disclosure relates to test and measurement instruments, inparticular to test and measurement instruments and methods of switchingwaveform display styles of the same.

Test and measurement instruments can be used to display waveformsassociated with information gathered from one or more electricalsignals. For example, a conventional oscilloscope can acquire electricalsignals through a particular channel, sample the electrical signals, anddisplay the sampled information as a waveform or overlapped waveforms.In one scenario, the oscilloscope can sample peak detect data, or inother words, minimum and maximum values within successive periods oftime and store these values in memory. In another scenario, theoscilloscope can apply lowpass filtering to the electrical signals anddisplay the lowpass sampled data in parallel with the peak detect data.Commonly-owned U.S. Patent Application Publication 2007/0217694 toSullivan et al. (hereinafter “Sullivan”), filed Mar. 20, 2006, entitled,WAVEFORM COMPRESSION AND DISPLAY, which is herein incorporated byreference in its entirety, discloses such a system.

Sullivan teaches that two waveforms can be overlaid. For example, aforeground waveform (i.e., filtered waveform) can be overlaid with abackground waveform (i.e., glitch capture waveform) so that bothwaveforms can be simultaneously observed. Traditionally, filtering hasinvolved a tradeoff. The waveform the user is looking at becomes cleanerand easier to measure, but the user loses the ability to see noise andhigh-frequency glitches. Sullivan avoids that trade-off by letting theuser see a filtered waveform along with the noise and glitches that werefiltered out. But Sullivan does not disclose how best to display thesesignals, or how to control their display, including how to turn one orthe other of them off.

SUMMARY

An embodiment is a test and measurement instrument comprisingacquisition circuits configured to acquire one or more data streams, andto generate peak detect data samples from the one or more data streams;input circuits configured to receive input from a user to change anamount of lowpass filtering applied to the one or more data streams; anda display unit configured to change the intensity of pixels associatedwith the peak detect data samples based on the proximity to pixelsassociated with lowpass filtered data samples for a given channel.Waveforms associated with the filtered or unfiltered data samples may beoverlaid on the related waveform associated with the peak detect datasamples.

Some embodiments include a method of switching waveform display styleson a test and measurement instrument including acquiring an electricalsignal; storing peak detect data samples from the electrical signal toone or more memory devices of the test and measurement instrument;storing filtered data samples or unfiltered data from the electricalsignal to the one or more memory devices; automatically switching to afirst waveform display style having the peak detect data samplesconfigured in a first mode when the user selects the unfiltered data;and automatically switching to a second waveform display style havingthe peak detect data samples configured in a second mode when the userselects the filtered data samples.

Another embodiment includes a method of electrical signal acquisitionand display, including digitizing the electrical signal to produce adata stream; compressing the data stream in parallel simultaneouslyusing a plurality of compression schemes, at least one of thecompression schemes being a lowpass filtering scheme, and at leastanother of the compression schemes being a peak detect compressionscheme, to produce a compressed sampled data stream for each compressionscheme; storing the compressed sampled data streams in one or morememory devices; generating a graphic waveform image associated with eachof the compressed sampled data streams; receiving an input from a userto adjust the lowpass filtering scheme of the sampled data stream; andchanging an appearance of the graphic waveform image associated with thepeak detect compression scheme when the user adjusts the lowpassfiltering scheme of the sampled data stream. The method may also includeshowing the graphic waveform image associated with the lowpass filteringscheme in a foreground of a display of a display device, and showing thegraphic waveform image associated with the peak detect compressionscheme in a background of the display of the display device.

Some embodiments include a method of displaying waveforms on a test andmeasurement instrument, including acquiring a first electrical signal ona first channel; acquiring a second electrical signal on a secondchannel; storing peak detect data samples for each of the channels toone or more memory devices of the test and measurement instrument;storing filtered data samples or unfiltered data for each of thechannels to the one or more memory devices; displaying pixels having afirst hue and first intensity that are associated with the filtered datasamples or unfiltered data for the first channel; and displaying pixelshaving a second hue and second intensity that are associated with thepeak detect data samples when a user selects the filtered data samplesfor the first channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a test and measurement instrument includingan acquisition unit, a controller, and a display unit having a waveformstyle selector according to an embodiment.

FIG. 2 is a block diagram illustrating additional elements of theacquisition unit of FIG. 1.

FIG. 3 is an example plot of a sampled electrical signal showingwaveforms having unfiltered data and peak detect data samples accordingto an embodiment.

FIG. 4 is an example plot of a sampled electrical signal showingwaveforms having filtered data samples and peak detect data samplesaccording to an embodiment.

FIG. 5 shows portions of the waveforms from the example plots of FIGS. 3and 4.

FIG. 6 shows portions of the waveforms from the example plots of FIGS. 3and 4.

FIG. 7 shows portions of the waveforms from the example plots of FIGS. 3and 4.

FIG. 8 shows portions of the waveforms from the example plots of FIGS. 3and 4.

FIG. 9 is a flowchart illustrating a technique of switching waveformdisplay styles on a test and measurement instrument of FIG. 1.

DETAILED DESCRIPTION

Embodiments include, for example, test and measurement instruments andtechniques of switching waveform display styles. In particular, in oneembodiment, the test and measurement instrument automatically switchesto a first waveform display style having peak detect data samplesconfigured in a first mode when the user selects unfiltered data, andautomatically switches to a second waveform display style having thepeak detect data samples configured in a second mode when the userselects filtered data samples.

FIG. 1 is a block diagram of a test and measurement instrument 100including an acquisition unit 102, a controller 120, and a display unit145. The display unit 145 may have a waveform style selector 142. Thetest and measurement instrument 100 may be an oscilloscope, for example,and for the sake of brevity but not limitation, will generally bereferred to as such. The oscilloscope 100 may have two channels suitablefor use with various embodiments as described herein. Although atwo-channel oscilloscope is shown, inventive aspects described areequally applicable to an oscilloscope having four channels, or anynumber of channels.

The acquisition unit 102 of the oscilloscope 100 may include a firstprobe 105 operatively associated with acquisition circuits 110 and asecond probe 107 operatively associated with acquisition circuits 115.The probe 105 and the probe 107 may be any conventional voltage orcurrent probes suitable for respectively detecting one or moreelectrical signals, such as analog voltage or current signals from acircuit under test (not shown). For example, the probes 105 and 107 maybe provided by Tektronix®, Inc., such as active probe model numbersP1075, TCP105, among others, which may be used to acquire real timeelectrical signal information. The output signals of probes 105 and 107are sent to the channel 1 acquisition circuits 110 and the channel 2acquisition circuits 115, respectively. The acquisition circuits 110 and115 sample and digitize the one or more electrical signals and storesampled data streams in memory, among other functions, as will be laterdescribed in further detail below. The acquisition unit 102 may beoperatively coupled to the controller 120.

The controller 120 is operatively coupled to the acquisition circuits110 and 115, and the display unit 145, and processes the sampled datastreams provided by the acquisition circuits 110 and 115 for display bythe display unit 145. For example, given desired time per division andvolts per division display parameters of the oscilloscope 100, thecontroller 120 may modify and then rasterize the raw data associatedwith an acquired sample data stream to produce a corresponding waveformimage having the desired time per division and volts per divisionparameters. The controller 120 may also normalize waveform data havingnon-desired time per division, volts per division, and current perdivision parameters to produce a waveform image having the desiredparameters.

The controller 120 preferably includes a processor 122, support circuits128, input/output (I/O) circuits 126, and memory 124. The processor 122is operatively coupled to the acquisition circuits 110 and 115. As such,it is contemplated that some of the processes discussed herein may beimplemented as software processes in processor 122, and some of theprocesses discussed herein may be implemented within hardware, forexample, as circuitry that cooperates with processor 122 to performvarious functions. In addition, some of the processes discussed hereinmay be implemented using a combination of software, hardware, firmware,or other execution or storage means. The I/O circuits 126 may form aninterface between the various elements communicating with the controller120. For example, the I/O circuits 126 may comprise an interconnectionto a keypad, pointing device, touch screen, external PC, or otherperipheral devices adapted to provide user input and output tocontroller 120. The controller 120, in response to such user input, maycontrol the operations of the acquisition circuits 110 and 115 toperform various functions, in particular filtering or other compressionoperations, but also including such operations as data acquisitions orprocessing, among other possibilities. In addition, the user input maybe used to trigger automatic calibration functions or provide controlfor other components included in, for example, the display unit 145.

The memory device 124 may include volatile memory, such as SRAM, DRAM,among other volatile memories. The memory device 124 may also includenon-volatile memory devices, such as a disk drive or a tape medium,among others, or programmable memory, such as an EPROM, EEPROM, or flashmemory, among other possibilities.

Although the controller 120 of FIG. 1 is depicted as a general purposecomputer or microprocessor that is programmed to perform various controlfunctions in accordance with embodiments of the present invention, theembodiments may be implemented in hardware such as, for example, anapplication specific integrated circuit (ASIC). As such, it is intendedthat the processor 120, as described herein, be broadly interpreted asbeing equivalently performed by hardware, software, or by anycombination thereof.

It will be appreciated by those skilled in the art that standard signalprocessing components (not shown), such as signal buffering circuitry,signal conditioning circuitry, display drivers, and the like are alsoemployed as required to enable the various interface functions describedherein. For example, the acquisition circuits 110 and 115 sample theelectrical signals under test at a sufficiently high rate to enableappropriate processing by the controller 120 or the processing circuits130 of the display unit 145. In this regard, the acquisition circuits110 and 115 may sample their respective input electrical signals inaccordance with a sample clock provided by an internal sample clockgenerator (not shown), which may be a part of, for example, the supportcircuits 128.

Controller 120 provides the waveform data to the display unit 145. Thedisplay unit 145 includes processing circuits 130 for subsequentpresentation of the waveform data on a display device 140. Theprocessing circuits 130 may include data processing circuitry suitablefor converting acquired data streams or waveform data into video imagesor video signals, which are adapted to provide visual imagery (e.g.,video frame memory, display formatting and driver circuitry, and thelike). The processing circuits 130 may interface with a memory 135, alsoincluded in the display unit 145, which may be arranged in memoryplanes, and may be configured to store the video images, among otherpossibilities. The processing circuits 130 and/or the memory 135 provideoutput signals suitable for use by a display device 140. User inputreceived through I/O circuits 126 may be used to adjust an amount offiltering to be applied to the sampled data streams, to triggerautomatic calibration functions, or to adapt other operating parametersof the processing circuits 130 and of display device 140. The displaydevice 140 may be configured to display the video images and to switchwaveform display styles responsive to the user input selection betweenlowpass filtered data samples and unfiltered data from among the datastreams, as will further be described in detail below.

The processing circuits 130 may include a waveform style selector 142.While the waveform style selector 142 is shown as part of the processingcircuits 130, it should be understood that the waveform style selector142 may be located elsewhere among other components of the oscilloscope100. For example, the controller 120 or the acquisition unit 102 mayinclude the waveform style selector 142, among other possibilities. Thewaveform style selector 142 may be implemented by hardware, software, orby any combination thereof. The waveform style selector 142 will befurther described in detail below with reference to FIGS. 3-9.

FIG. 2 is a block diagram illustrating additional elements of theacquisition unit 102 of FIG. 1 according to an embodiment. Theacquisition unit 102 may include circuitry for one or more channels.Although the circuitry for only two channels is shown, the oscilloscope100 may have any number of channels and associated components. Eachchannel has associated therewith acquisition circuits (e.g., 110 and115). The acquisition circuits include analog-to-digital converters(ADCs) (e.g., 205 and 245), which collectively sample the electricalsignals received through the respective probes (e.g., 105 and 107). TheADCs deliver data streams to a sampler (e.g., 210 and 250). The samplermay include a decimator circuit (e.g., 220 and 260), lowpass filters(e.g., 225 and 265), and peak detectors (e.g., 230 and 270), among otherpossible components.

The peak detectors generate peak detect data samples by finding themaximum and minimum values within successive periods of time, and maystore these values in one or more memory devices (e.g., 215 and 255).The lowpass filters remove high frequency components of the electricalsignals, and may generate lowpass filtered data samples to be stored inthe one or more memory devices. The decimator circuit provides a form ofcompression by discarding samples. For example, to compress by a factorof ten, the decimator circuit just discards nine out of every tensamples. (Other fractions, such as one of eight samples, can be used).Any one or more of the peak detectors, lowpass filters, and decimatorcircuits may be applied in parallel simultaneously to the data streamsto produce peak detect data samples, filtered data samples, and/orcompressed data. In some embodiments, for example, only the peakdetectors and the decimator circuits are used to modify the datastreams, while leaving the data streams unfiltered. In otherembodiments, the lowpass filters are applied to the data streams toproduce the filtered data samples, which may also be decimated orotherwise further compressed. In still other embodiments, the decimatorcircuits compress at least some of the unfiltered data and the filtereddata samples. In any case, the resulting samples, whether filtered orunfiltered, compressed or not compressed, may be stored in the one ormore memory devices, and used with the various embodiments discussedherein. Graphic waveforms may then be generated that are associated witheach of the sampled data streams.

Although the decimator circuits, lowpass filters, and peak detectors areshown as individual circuits, they may be designed as a single unit, orfor example, two units. The peak data samples may be “tagged” asbackground data for display and the decimated or lowpass filtered datamay be “tagged” as foreground data for display. The peak detect datasamples, in addition to providing information about the peak-to-peaksignal amplitude, may be viewed as warning information such as warningthat a narrow pulse occurred, a high frequency signal is present, orthat the dynamic range of the ADCs is being exceeded. The informationstored in the acquisition memory devices (e.g., 215 and 255) may betransmitted to the processor 122 (of FIG. 1). In addition, the processor122 may transmit control information to the acquisition unit 102.

FIG. 3 is an example plot 300 of a sampled electrical signal showingwaveforms having unfiltered data 320 and peak detect data samples 310according to an embodiment. FIG. 4 is an example plot 400 of a sampledelectrical signal showing waveforms having filtered data samples 420 andpeak detect data samples 410 according to an embodiment. The followingdescription will now be given with reference to both of FIGS. 3 and 4.

Traditionally, filtering waveforms on an oscilloscope has involved atrade-off. The waveform the user is looking at becomes cleaner andeasier to measure, but the ability of the user to see noise andhigh-frequency glitches is diminished or lost. As mentioned above,Sullivan discloses a technique for displaying a foreground filteredwaveform overlaid with a background glitch capture waveform. In thismanner, both waveforms can be viewed simultaneously, which is moreuseful than a single filtered waveform.

However, a certain kind of users may want the oscilloscope to drawwaveforms in a way that is similar to the way oscilloscopestraditionally operate. This category of users would not particularlycare about the glitch capture background or other peak data samples, andwould not want to think about the difference between the foreground andbackground waveform. Another kind of users may want the ability to seeboth filtered data and glitch data on the display and be able todifferentiate between the foreground and background waveforms. It isimportant to these users that the two waveforms are visually distinct.Of course, any of the users, in the examples given above, can switchbetween being either of the two kinds of user, depending upon the workthat is being done at a particular moment.

To address the conflicting requirements, the example embodiments of thepresent invention provide various methods for automatically displayingthe peak detect data samples in the background in either “quiet” or“loud” peak detect modes. The oscilloscope uses quiet peak detect whenfiltering is off, and loud peak detect when filtering is on. Preferably,the oscilloscope switches between these two modes of operationautomatically, rather than forcing the user to independently choose adisplay method.

In FIG. 3, the waveform is shown in “quiet” peak detect mode.Preferably, this is the oscilloscope's default mode of operation. Inthis mode, pixels associated with the peak detect data samples 310 aredrawn using a same hue as pixels associated with the unfiltered data320. In addition, the pixels associated with the peak detect datasamples 310 can be drawn with an intensity that substantially matchesthe intensity of the dimmest pixel from among the pixels associated withthe unfiltered data 320 when the user selects the unfiltered data 320.“Substantially matches” means that the intensity is similar to or thesame as, but need not be an exact match. The “fuzz” and “spikes” aroundthe waveform are either from the peak detect data samples 310 displayedin the background, or from the unfiltered data 320 in the foreground. Inthe quiet peak detect mode of operation, two overlaid waveforms (i.e.,associated with the peak detect data samples and the unfiltered data)can appear as one seamless waveform. Even though the user may be unableto tell which is which, such differentiation does not matter in thismode.

It should be understood that while the data 320 is referred to as“unfiltered,” the data 320 can nevertheless be compressed using, forexample, the decimator circuit (e.g., 220 and 260 of FIG. 2) describedabove. As used herein, the terms “filtered” and “unfiltered” refer towhether, or how much, lowpass filtering is applied to the electricalsignal using, for example, lowpass filters 225 or 265 (of FIG. 2). Theportion 340 of the waveform will be described in more detail below.

In FIG. 4, the waveform is shown in “loud” peak detect mode. This modeis used whenever the foreground waveform 420 is filtered. The loud peakdetect mode shows pixels associated with the peak detect data samples410 in a different hue (i.e., color) and/or intensity (i.e., brightness)from those used to display pixels associated with the filtered datasamples 420 shown as the foreground waveform. That is, the loud peakdetect mode pixels are shown having a hue that is shifted slightly fromthe hue of the foreground waveform, giving it a similar, but distinct,appearance. Additional details regarding the shifting of hues are givenbelow with reference to FIGS. 6-8. This makes it easy for the user todistinguish the two waveforms. In areas of the screen in which the peakdetect data samples forming the background waveform 410 are within adistance of a few pixels from the foreground waveform 420, the intensityof the background waveform is dimmed, in that area only, to furtherenhance the contrast. That is, a “guard band” or “trench” 430 may beplaced on either side of the foreground waveform 420 so that the usercan more easily see the foreground waveform.

Once again, note that the foreground waveform 320 in FIG. 3 isunfiltered, whereas the foreground waveform 420 of FIG. 4 is filtered.When filtering is off, the waveform style selector 142 (of FIG. 1) maydisplay waveforms using the quiet peak detect mode. Conversely, whenfiltering is on, the waveform style selector 142 may display waveformsusing the loud peak detect mode.

For example, the pixels associated with the peak detect data samples 410that are proximally located to pixels associated with the filtered datasamples 420 may be dimmed responsive to the location of thecorresponding lowpass filtered waveform image pixels. In other words,the resulting image will respond to user changes in the amount oflowpass filtering applied. As another example, the waveform styleselector 142 of the processing circuits 130 (of FIG. 1) mayautomatically switch to a first waveform display style 300 having thepeak detect data samples 310 configured in a first mode when the userselects the unfiltered data 320. The user may select the unfiltered data320 by adjusting an input of the oscilloscope 100, the input of whichmay use, for example, the I/O circuits 126 (of FIG. 1). Similarly, thewaveform style selector 142 of the processing circuits 130 (of FIG. 1)may automatically switch to a second waveform display style 400 havingthe peak detect data samples 410 configured in a second mode when theuser selects the filtered data 420. Again, the user may select thefiltered data 420 by adjusting an input of the oscilloscope 100, theinput of which may use, for example, the I/O circuits 126 (of FIG. 1).

By switching display styles, the oscilloscope 100 shows the waveform inthe way that is most useful to the user. The user does not need to takeadditional action to adjust the display style to be suitable.

FIG. 5 shows portions 340 and 440 of the waveforms from the exampleplots of FIGS. 3 and 4 according to one embodiment. In the portion 340,the waveforms include unfiltered data 320 shown in the foreground withthe peak data samples 310 next to the unfiltered data 320, which are inthe background. This corresponds to the “quiet” peak detect mode asdescribed above. In the portion 440, the waveforms have transitioned tothe “loud” peak detect mode responsive to the user selecting thefiltered data samples 420 for display on the display device 140 (of FIG.1). The waveforms in this portion include the filtered data samples 420and lower intensity peak data samples 430 forming the “guard bands” or“trenches” between the filtered data samples 420 and the peak datasamples 410. For example, the peak detect data samples 410 that arewithin a distance of a few pixels from the filtered data samples 420, orotherwise proximally located to the filtered data samples 420, may bedimmed in that area only, to further enhance the contrast between thefiltered data samples 420 and the peak detect data samples 410. In otherwords, the appearance of a graphic waveform image associated with thepeak detect data samples 430 can possibly be changed when the useradjusts the lowpass filtering scheme of a sampled data stream,reflecting changes in the underlying filtered waveform data.

FIG. 6 shows portions 340 and 440 of the waveforms from the exampleplots of FIGS. 3 and 4 according to another embodiment. The portion 340includes waveforms having the unfiltered data 320 and the peak datasamples 310 in the “quiet” peak detect mode. In this embodiment, theuniform hue #1 is applied to both the unfiltered data 320 and the peakdata samples 310. The portion 440 includes waveforms having the filtereddata samples 420, the lower intensity peak data samples 430 forming the“guard bands” or “trenches” about the filtered data samples 420, and thepeak detect data samples 410 in the “loud” peak detect mode. After (orwhile) transitioning to the loud peak detect mode, a second hue #2 isapplied to only the peak detect data samples 410, including the lowerintensity peak data samples 430. In other words, a hue of the pixelsassociated with the peak detect data samples 410 may be changed when theuser of the oscilloscope 100 selects the filtered data samples 420 fordisplay, or when the user of the oscilloscope 100 selects the unfiltereddata 320 for display.

The result is that the loud peak detect mode is automatically engagedand provides waveforms primarily showing the underlying filtered signal,absent the noise, while the peak detected data samples show primarilythe peaks of the noise. The displayed waveforms allow the user to see asignal having a bright intensity and suitable hue in the foreground, andto see the noise in a dimmer intensity and secondary hue in thebackground. While FIG. 6 shows that pixels associated with theunfiltered data 320 and the filtered data samples 420 are of the samehue, in an alternative embodiment, pixels associated with the unfiltereddata 320 are displayed having a hue and intensity that are differentfrom the pixels associated with the filtered data samples 420.

Regarding the hues #1 and #2, these may be selected from a color wheelrotation so that they are most pleasing to the eye. The color wheel (notshown), as used herein, refers to an organization of color hues around acircle, having relationships between at least colors considered to beprimary colors and secondary colors, as is known in the prior art.Preferably, the hue #1 is selected from a group comprising yellow, cyan,magenta, and green. These colors are preferred because the human eye canmore easily perceive them. The hue #2 can be shifted by about 30 degreeson the color wheel rotation from the hue #1.

For example, if yellow at about 60 degrees on the color wheel isselected for hue #1, then hue #2 will preferably correspond to orange atabout 30 degrees on the color wheel. If cyan at about 180 degrees on thecolor wheel is selected for hue #1, then hue #2 will preferablycorrespond to sky blue at about 210 degrees on the color wheel. Ifmagenta at about 300 degrees on the color wheel is selected for hue #1,then hue #2 will preferably correspond to light purple at about 270degrees on the color wheel. If green at about 120 degrees on the colorwheel is selected for hue #1, then hue #2 will preferably correspond tomustard at about 90 degrees on the color wheel.

As previously mentioned, the oscilloscope 100 can have multiplechannels. If, for example, the oscilloscope 100 has four channels, eachof the channels can have associated therewith one of the hues selectedfrom the group comprising yellow, cyan, magenta, and green. Further, thepeak detect data samples for each of the channels may be stored to theone or more memory devices of the oscilloscope, along with the filtereddata samples or unfiltered data for each of the channels. Then, for agiven channel, the oscilloscope can display pixels having a first hue(e.g., yellow, cyan, magenta, or green) and first intensity that areassociated with the filtered data samples or unfiltered data, and candisplay pixels having a second hue (e.g., orange, sky blue, lightpurple, or mustard) and second intensity that are associated with thepeak detect data samples when the user selects the filtered data samplesfor the given channel. Generally, the second intensity will be dimmerthan the first intensity, at least for some of the pixels, because thesecond intensity may correspond to the “guard bands” or “trenches.”Similar hue and intensity configurations can be applied for each of thechannels.

FIG. 7 shows portions 340 and 440 of the waveforms from the exampleplots of FIGS. 3 and 4 according to yet another embodiment. Theseportions are similar to those discussed above; therefore, for the sakeof brevity, a detailed description will be omitted. However, it shouldbe noted that in this embodiment, three different hues may be used todifferentiate the different elements of the waveforms. For example, inportion 440, hue #1 may be applied to the filtered data samples 420, hue#3 may be applied to the lower intensity peak data samples 430 that areproximally located to pixels associated with the filtered data samples420 when the user selects the filtered data samples 420 for display, andhue #2 may be applied to the peak data samples 410 that are moredistantly located to pixels associated with the filtered data samples420 than the proximally located pixels 430 when the user selects thefiltered data samples 420 for display. Hues #1, #2 and #3 can correspondto any hues and need not correspond to hue #1 and hue #2 of FIG. 6.

FIG. 8 shows portions 340 and 440 of the waveforms from the exampleplots of FIGS. 3 and 4 according to still another embodiment. Theseportions are also similar to those discussed above; therefore, for thesake of brevity, a detailed description will be omitted. Here, it shouldbe noted, however, that gradients of colors may be applied to thewaveforms. For example, color gradient #1 may be applied to the peakdata samples 410 extending outwardly from the pixels associated with thefiltered data samples 420 when the user selects the filtered datasamples 420 for display. Similarly, color gradient #2 may be applied ina similar fashion, but extending outwardly in the opposite direction.

FIG. 9 is a flowchart illustrating a technique of switching waveformdisplay styles on an oscilloscope according to some embodiments. Theprocedure may begin by acquiring an electrical signal at 900. Theelectrical signal may then be processed. For example, peak detect datasamples and filtered data samples and/or unfiltered data may besimultaneously generated at 910 and 920 from the acquired electricalsignal. At 930, the user may adjust an input of the oscilloscope toselect unfiltered data. If the user indeed selects unfiltered data fordisplay at 930, the flow proceeds to 940 and the display is switched toa first waveform display style having the peak detect data samplesconfigured in a first mode. Otherwise, if the user selects filtered dataat 950, the display is switched to a second waveform display stylehaving the peak detect data samples configured in a second mode. Ineither case, the flow continues through ‘A’ such that the oscilloscopecontinues to acquire an electrical signal, to store peak detect datasamples and filtered data samples and/or unfiltered data, and to monitorthe input of the oscilloscope for selection by the user of filtered orunfiltered data for display. As described thoroughly above, theappearance of the peak detect data samples is automatically adjustedaccording to the selection of the user of filtered data samples and/orunfiltered data.

Although particular embodiments have been described, it will beappreciated that the principles of the invention are not limited tothose embodiments. Variations and modifications may be made withoutdeparting from the principles of the invention as set forth in thefollowing claims.

The invention claimed is:
 1. A digital oscilloscope, comprising: inputchannels for receiving analog input data streams applied to said digitaloscilloscope; acquisition circuits, coupled to respective ones of saidinput channels of said digital oscilloscope, each of said acquisitioncircuits including an A/D converter, configured to acquire one or moreof said analog input data streams, and to generate peak detect digitaldata samples and unfiltered data samples and lowpass filtered datasamples from one or more of said analog input data streams; inputcircuits configured to receive input from a user to change an amount oflowpass filtering applied to one or more of said analog input datastreams; and a display unit having first and second modes, the firstmode displaying a first combined waveform in which the peak detectdigital signal data samples are overlaid with the unfiltered datasamples, and the second mode displaying a second combined waveform inwhich the peak detect digital signal data samples are overlaid with thelowpass filtered data samples, the display unit being configured tochange an intensity of pixels associated with the peak detect digitaldata samples based on the proximity to pixels associated with thelowpass filtered data samples for a given input channel; wherein saiddisplay unit includes: processing circuits configured to convertwaveform data associated with the peak detect data samples, unfiltereddata samples and the lowpass filtered data samples into the first orsecond combined waveform display images; a memory to store datarepresentative of the first or second combined waveform display images;and a display device configured to display the waveform display imagesby automatically selecting the first or second m responsive to a userselection between the lowpass filtered data samples and the unfiltereddata samples.
 2. The digital oscilloscope of claim 1, wherein theacquisition circuits include: at least one lowpass filter configured togenerate the filtered data samples; at least one peak detectorconfigured to generate the peak detect data samples; and at least onedecimator circuit configured to compress at least some of the unfiltereddata and the filtered data samples.
 3. The digital oscilloscope of claim1, wherein the display unit is configured to form trenches between thepixels associated with the peak detect data samples and the pixelsassociated with filtered data samples.
 4. The digital oscilloscope ofclaim 1, wherein the intensity of the pixels associated with the peakdetect data samples substantially matches a dimmest pixel from amongpixels associated with unfiltered data responsive to the user selectingthe unfiltered data.
 5. The digital oscilloscope of claim 1, furthercomprising a controller operatively coupled to the acquisition circuitsand the display unit, and configured to process the one or more datastreams and to generate respective waveform data.
 6. The digitaloscilloscope of claim 3, wherein the trenches include dimmed pixelsassociated with the peak detect data samples that are proximally locatedto the pixels associated with the filtered data samples.